Check the flywheel key, if it sheared off, there will be spark, but it won't come at the right time. Next, I would pop one of the inpection caps off the vavle cover and make sure your vavles are moving when you turn the motor over, it would also be a good idea to check your valve lash while you have the covers off, if the valves are too tight, it could cause hard starting. I would also try putting in a fresh plug. Also, inspect the coil wire, unscrew the boot from the wire itself and look at the wires inside the insulation, and check along the length of the wire for cracks or worn spots in the insulation. Make sure there is plenty of good wire at the end for the screw in the boot to make contact with. Most shops will tell you that the best way to test a CDI is to replace it with a known good unit. The best thing you can do IMO, is get a repair manul, it should have several tests for many of the electrical components, including your rectifier. It will also have vavle clearance specs and bolt/nut torquing info, all stuff you need to have if you are working on your own machine.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.